Aggregation-induced emission poly(meth)acrylates for photopatterning via wavelength-dependent visible-light-regulated controlled radical polymerization in batch and flow conditions

A robust wavelength-dependent visible-light-regulated reversible-deactivation radical polymerization protocol is first reported for the batch preparation of >20 aggregation-induced emission (AIE)-active polyacrylates and polymethacrylates. The resulting polymers possess narrow molar mass distributions (Đ ≈ 1.09–1.25) and high end-group fidelity at high monomer conversions (mostly >95%). This demonstrated control provides facile access to the in situ generation of complex sequence-defined tetrablock copolymers in one reactor, even while chain extending from less reactive monomers. Polymerizations can be successfully carried out under various irradiation conditions, including using UV, blue, green, and red LED light with more disperse polymers obtained at the longer, less energetic, wavelengths. We observe a red shift and wavelength dependence for the most efficient polymerization using LED illumination in a polymerization reaction. We find that the absorption of the copper(II) complex is not a reliable guide to reaction conditions. Moreover, the reported protocol is readily translated to a flow setup. The prepared AIE-active polymers are demonstrated to exhibit good photopatterning, making them promising materials for applications in advanced optoelectronic devices

Functional pH-responsive polymers containing dynamic enaminone linkages for the release of active organic amines

Dynamic covalent bonds have attracted considerable attention for the development of pH-responsive polymers, however, studies using acid-cleavable enaminone linkages as a means of controlled release are limited. Herein, we report pH-sensitive benzocaine-modified poly(ethylene glycol) monomethyl ether-block-poly[2-(acetoacetoxy)ethyl methacrylate] (mPEGx-b-pAEMAy)/BNZ nanoparticles (NPs) for the aqueous controlled release of benzocaine through enaminone bond cleavage. The system is based on the commercially available monomer 2-(acetoacetoxy)ethyl methacrylate (AEMA) which contains free pendant β-ketoester functionality. Well-defined poly[2-(acetoacetoxy)ethyl methacrylate] (pAEMA) homopolymers and poly[(ethylene glycol) monomethyl ether]-block-poly[2-(acetoacetoxy)ethyl methacrylate] (mPEGx-b-pAEMAy) amphiphilic block copolymers were prepared by photoinduced Cu(II)-mediated RDRP to investigate their modification with propylamine (a model amine) and benzocaine (a primary amine containing API) through an enaminone bond. Block copolymers were prepared via two poly(ethylene glycol) monomethyl ether-2-bromo-2-phenylacetate (mPEGx-BPA, x = 43 or 113) macroinitiators synthesised by esterification which acted as the hydrophilic coronas of the ensuing NPs. The self-assembly of both mPEGx-b-pAEMAy and (mPEGx-b-pAEMAy)/BNZ was assessed in water by the direct dilution approach forming spherical NPs as characterised by dynamic light scattering (DLS) and dry-state transmission electron microscopy (TEM). Finally, the in vitro controlled release of benzocaine from mPEGx-b-pAEMAy/BNZ NPs was examined at different pH environments demonstrating faster release kinetics at lower pH with potential utility in applications with relevant chemical environments

Well-defined polyacrylamides with AIE properties via rapid Cu-mediated living radical polymerization in aqueous solution : thermoresponsive nanoparticles for bioimaging

There is a requirement for the development of methods for the preparation of well-controlled polymers with aggregation-induced emission (AIE) properties. This requirement directed this current work towards a robust synthetic route, which would be applicable for preparation in water and the presence of many types of functional groups. Herein, aqueous Cu-mediated living radical polymerization (LRP) has been optimized to provide facile and rapid access to a diverse range of water-soluble AIE polymers at sub-ambient temperatures. Homo-, block and statistical copolymerization all proceeded to a near full monomer conversion (≥99%) within 1 or 2 h and exhibited narrow dispersity, even when DP was targeted up to 1000. This excellent control associated with this polymerisation technique and the high-end group fidelity achieved were further demonstrated by linear first order kinetics and successful in situ block copolymerization, respectively. Fine-tuning the monomer sequence and composition of poly(N-isopropylacrylamide) (PNIPAM) copolymers allows for different lower critical solution temperature (LCST) and fluorescent thermoresponsive nanoparticles, which spontaneously self-assembled to varying sizes in water as determined by a combination of techniques (DLS, SAXS and TEM). Additionally, the fluorescence intensity was demonstrated to depend on the polymer concentration, architecture of the side chains and temperature. Particularly, PNIPAM-containing polymers were resistant to reduction in thermo-induced emission. The good biocompatibility, photostability and high specificity make them promising candidates as lysosome-specific probes for application in bioimaging

AIE-active polymers via copper mediated reversible deactivation radical polymerization

Molecular aggregation had been regarded to be detrimental to luminescence due to aggregation-caused quenching (ACQ) phenomenon. Intriguingly, the concept of aggregation-induced emission (AIE) has revolutionarily demonstrated that aggregation allows for boosted light emission with an appropriate chemical moiety, contributing potential applications. However, there is a requirement for the development of facile synthesis of well-defined and narrow-dispersed AIE polymers. As a robust polymerization technique, Cu(0)-mediated reversible deactivation radical polymerization (Cu(0)-RDRP) allows good control over diverse molecular weight, topology and chain length distributions under mild conditions. In this work, 3 different Cu(0)-RDRP techniques are extensively applied to generate well-defined AIE-active polymers by using an AIE-containing initiator tetraphenylethene bromoisobutyrate (TPEBIB). These synthesized TPE-terminated polymers with a range of molecular weights and diverse architectures are all demonstrated to be AIE-active, possessing narrow molar mass distributions and high end-group fidelity at high monomer conversions. This control also provides facile access to in situ generation of block copolymers. In chapter 2, Cu(0)-wire mediated RDRP was firstly employed for the construction of different polyacrylates. Some copolymers can self-assemble in aqueous media forming fluorescent nanoparticles with various sizes, which can work as lysosome-specific probes in biological imaging. In chapter 3, aqueous Cu-mediated RDRP with pre-disproportionation of Cu(I) was optimized to provide facile and rapid access to water-soluble AIE polyacrylamides at sub ambient temperatures. Some thermoresponsive polymers can spontaneously self assembled into fluorescent nanoparticles with a suitable size at physiological conditions, applicable for lysosome-specific cell imaging. Broad interest in light-mediated RDRP arises as it allows for spatial and temporal control over reaction kinetics, monomer sequences and compositions. In chapter 4, we present the synthesis of AIE-active polymers involving >20 different monomers with diverse architectures initiated by TPEBIB using visible-light regulated RDRP in both batch and flow reactors. These AIE-active polymers exhibit good photo-patterning, making them promising materials for advanced optoelectronic device

Guia do camponês: pragas & doenças da banana

Este livrete fala sobre todas pragas e doenças da banana. Ele te narra como elas se presentam, se propagem e como controlá-las. Estamos le dando este livrete como um agradecimento de ter participado no leventamento feito por um de nós. Esperamos que isso vai ajudar você a lembrar do que você estudou durante o levantamento e descobrir mais sobre outras doenças

Superbase/saccharide: An ecologically benign catalyst for efficient fixation of CO2 into cyclic carbonates

An ecologically benign catalytic system consisting of superbase and saccharide was developed for CO2 chemical fixation with epoxides under metal-free and halide-free conditions. Because of the synergistic effect played by superbase and saccharide on the activations of CO2 and epoxide, the reaction could be performed with good activity and selectivity. A possible catalytic mechanism of the hydrogen-bonding of saccharide and activation of the carbon atom by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was proposed. The process is a simple, biocompatible, and ecological route for CO2 chemical fixation into high-value chemicals

Tailoring Molecular Weight of Bioderived Polycarbonates via Bifunctional Ionic Liquids Catalysts under Metal-Free Conditions

Synthesis of bioderived high-molecular-weight polycarbonates over metal-free catalysts is of great importance but also challenging. In this work, a series of 1-butyl-3-methylimidazolium (Bmim) ionic liquids (ILs) were prepared as catalysts for a melt polycondensation reaction of isosorbide and diphenyl carbonate. By modifying the structures of ILs&#39; anions, the number-average molecular weight (M-n) of poly(isosorbide carbonate) (PIC) was effectively tailored. In the presence of a trace amount (0.05 mol % based on isosorbide) of bifunctional [Bmim][CH3CHOHCOO], the synthesized PIC possessed high M-n of 61,700 g/mol and a glass transition temperature of 174 degrees C, both the highest so far to the best of our knowledge. Besides, it was found that the anions with stronger electronegativity and hydrogen bond formation ability were more efficient for the formation of PIC with higher M-n. To modify the flexibility of PIC, poly(aliphatic diol-co-isosorbide carbonate)s with M-n ranging from 34,000 to 75,700 g/mol were also formulated by incorporating with various aliphatic diols. Additionally, based on the experimental results and nuclear magnetic resonance spectroscopy, a possible mechanism of cooperative nucleophilic-electrophilic activation through hydrogen bond formation and electrostatic interactions by the ILs catalyst was proposed.</p